sorry for posting another driveway question - a few have been answered
pretty thoroughly in the past couple of days.
This question concerns a driveway/private road that I'm going to build on
a steep(~20%) grade about 675 feet long. The current plan is to use two
3' wide strips of concrete 4 inches thick for the driving surfaces leaving
a 26" open span in the center(or possibly covered with a sheet of thin
concrete to prevent erosion). The reason for this design was price is and
has been a stumbling block. So my first question would be, do these
dimensions make sense and second, what do you think of the idea of going
with two strips of concrete on a steep hill? Is that going to be
Another thing we need is good drainage and the drainage probably needs to
cross the road at some point. Any ideas? As for the soil all this will
be resting on, the best I can describe it is a rocky red clay.
Any input will be greatly appreciated,
On Wed, 15 Nov 2006 12:39:06 +0000, kickstart wrote:
OK. It's a bit of a maze but I think I can keep it between 5" and 6"
without price becoming prohibitive.
Ah, which brings up a good point. We had a culvert pipe about 14" wide
get clogged a few years back. Now it's solid from what I can tell. If
I'm building this with two slabs of concrete, can I simply make the side
culvert cross under the road, albeit a bit deeper and make the slabs
thicker(maybe 8" thick with 2 pieces of 1/2" rebar) where they cross as
bridges? The bridge span would be about 3 feet and I'd have plenty of
room to clear debris this way.
On Wed, 15 Nov 2006 15:43:34 +0000, Bob Morrison wrote:
Thanks for the reply,
I didn't really refer the the grade properly. Thankfully, it's not all
20% grade and it's certainly not at the beginning nor at the end, but a
few sections in the middle are very steep. The weather is tropical so no
there is no frost/freezing but it is near the beach so I think I'm
considering not using metal(thanks Bob). My rational is that not using
reinforcement will be cheaper and there will be no chance for it to rust
which on a thin slab with so-so drainage and hand mixed concrete seems
OK, 5" and no center slab. How about the road dimensions. Is there a
standard for double slab roadways like this? I came up with those
measurements (two 3' wide strips 26" apart) by getting under the car with
a tape. I'm not really sure how much other vehicles may vary.
Is every sixty feet OK for expansion joints and would you have any
thoughts on what type of prep work I will need? Keep in mind I'm doing
this in a small town in South America and we don't have any heavy
machinery available. It will be done with a pick and shovel and a LOT of
I have used GFRP reinforcing in elevated slabs in tropical climates, but
it is expensive. So, I think going unreinforced is a excellent idea.
Compact car parking spaces are often 8 feet wide. This is probably a
little narrow for a driveway, but if the driver is at all decent, 8'-6"
could be okay. I'd probably go no less than 9 feet minimum to allow for
the occasional small truck or delivery van.
End of pour cold joints can be 100 feet apart or so. This kind of joint
will be full depth and will have a shear key and some oiled dowels to
transfer shear across the joint. Crack control joints should be every 12
to 15 feet. These joints are usually tooled or sawcut and are 1" deep.
For hand mixed concrete you will probably not be able to pour more than
9'x 14' in a day. So, it won't be necessary to cut crack control joints,
but you will need some method for transferring shear between one day's
pour and the next.
For compaction of subgrade, use a loaded dump truck or other heavy
vehicle. For compaction of gravel base see if you can rent a Jumping
Jack. If not then you can run the heavy truck over the gravel and use
hand compaction methods for as needed.
Bob Morrison, PE, SE
R L Morrison Engineering Co
On Wed, 15 Nov 2006 18:03:55 +0000, Bob Morrison wrote:
Alright, 9 feet wide sounds reasonable.
Researching a bit I've found some details described here concerning shear
keys and oiled dowels in addition to how to make various connections
between pours. Do you think an oiled dowel joint would be sufficient?
From work we've done in the past, your estimate(9'x14'x5"= 52.5cft) seems
reasonable but I've got to figure out a way to do much more.
Otherwise(according to my calculations) it will take 38 days to pour the
slabs alone. The plan is to start at the top and work our way down
because materials can be dropped at the top and it's easier to move them
downhill than up. Also it's going to help if at least some people can use
the top portion of the road before the lower section is able to be driven
If a heavy truck were to be used for compaction, how deep of a gravel bed
do I want(and what size gravel should be used?) As for actually
compacting the gravel, I'm curious how that works. Are the rocks really
getting pressed together tighter or are they being pressed into the
topsoil?? Sorry for asking such basic questions but from what I
gather this stage is crucial to the longevity of the drive and I'm
pretty fuzzy on it's function in general. I also worry about water
undermining the entire road if it seeps below the slab in places such as
the uncovered center section. Is this a legitimate concern?
For light traffic an oiled dowel w/o shear key is probably okay.
You want to end up with 6" of compacted thickness. I usually recommend
3/4" minus crushed rock. If you are concerned about pushing the gravel
into soft soil then use a geotextile between the gravel and soil.
Otherwise, compact the soil first then apply and compact the gravel layer.
The gravel layer is intended to be free-draining. Water should pass
through it. You could excavate a deeper section in the middle of the an
install a "french" drain, but given the slope of the driveway I don't
think water will be of much concern as long as you have drainage ditches.
Bob Morrison, PE, SE
R L Morrison Engineering Co
On Thu, 16 Nov 2006 00:11:24 +0000, Bob Morrison wrote:
Would it take much extra effort or cost much more to make dowel joints
with shear keys at the end of each day? Is anything special used to
separate the old and new pours or do I just place the new pour up against
the old with oil on the (painted?) dowels side of the new pour?
The drainage ditch will only be on one side at a time but along the entire
length of roadway and I'll need to switch it from the uphill side to the
downhill side at about the halfway point which I figure means a bridge.
How thick should the two 3.5' wide sections be in order to support an
occasional truck for a span of 3 feet over air? And if you don't mind me
asking, how much reinforcement will be needed there as well?
Bob, thanks for all your help! You've already made a significant
difference in the project.
Since you are going to be making lots of these joints you may wish to buy
preformed metal shear keys with holes punched for the dowels. Something
Or perhaps you can get a local welder to make up something.
Here's a link describing how joints in concrete should work:
Think about using a plastic or metal culvert (or culverts) instead of
making a bridge. They should be buried with at least 12 inches of
gravel/dirt cover below the bottom of the concrete.
Bob Morrison, PE, SE
R L Morrison Engineering Co
On Thu, 16 Nov 2006 15:58:50 +0000, Bob Morrison wrote:
Well, we have a welder as one of the group of 5 taking on this challenge
and I'm pretty sure he has access to material so I'll ask if he can weld
up two short 3.5' keys and drill holes in them for dowels. From the link
you sent I can see that the dowels are pretty substantial but I can't find
a size. How large should they be if I have a 6" slab with shear key?
OK, I'll have to think about a design to keep the culvert clean because
the last effort(12 years ago and super shoddy construction) had a 14"
galvanized culvert which filled up solid due to rocky debris getting stuck
in it when it rained hard. If I can pull it out and reuse it I'd be set,
but so far I haven't come up with any real imaginative plan to do that.
Best I have is lots of guys with picks and some rope. ;) But then that
might just be what it takes.
I'm creating a materials list now and have a specific question pertaining
to concrete mixture. We use 42.5 kg sacks of Portland type 1 cement, 3/4"
minus crushed granite with clean & sharp sand. Do you(or anyone else
reading this thread) have a mixture recommendation for building a STRONG
6" slab using these materials?
As I recall, the driveway is to be 9' wide, so with 7' total of
pavement width that leaves 2' of clear space in the middle. What is
the advantage of this configuration over a single 9' wide drive? Is
it simply the 2/9 materials savings, or is there some other advantage?
It was already stated that cost was a major factor. They will be
trading off concrete for twice the form work, but, apparently
labor is easier to come by than $$$.
Keep the whole world singing. . . .
Well, of course I wish cost wasn't such a major factor but with a 675 foot
drive like this(plus drainage) it really is. We could try to put it off
another year or two but at this point the road is simply impassible at
times and it really sets us back.
Oddly enough, there is one 50 foot section of the original driveway still
intact and it's the one section that was double lane. I wouldn't really
know, but my hypothesis is that being able to move independently may have
helped that section survive 12 years of harsh weather and erosion. I feel
like that is going out on a limb but it does strike me as odd.
As DanG mentioned already, labor is relatively inexpensive here(Mochima,
Venezuela). Concrete isn't that bad but transportation out to the middle
of nowhere is. And that goes for rocks and sand too.
This link below is a picture that gives a(very rough) idea of the
goegraphy where the road/driveway will be built. The houses on the far
side of the bay(or right side of the bay perhaps) are the ones the drive
will affect directly. I'm at the bottom so I REALLY need it.
Hmmm, let's see. Beautiful location, guy posting is involved with
eco-tourism diving, needs expert help with a project. Who's up for a
field trip to help this guy build this thing? I figure we can bang it
out in three or nine years. Lodgings and Margaritas are on Chuck ;)
On Fri, 17 Nov 2006 20:38:39 -0800, RicodJour wrote:
Oh, classic! That's the spirit!!!
Around here we have a term for what you are proposing, although it's
unofficially limited to a weekend. A "fajina" is a party whereby you give
guests food, drink and lodging in exchange for their abundant cooperation
on what otherwise would be an impossible task.
Come to think of it, I bet I know how to rip that culvert out of the
ground now. ;p
Oh, sure. Go ahead and use essentially free local labor that'll have
it done in a weekend and have a big party instead of flying in some
gringos that will suck down food, drink and take up space for years.
That makes _no_ sense...for me. And, if I may say so, it's
particularly un-South American. I wish you'd reconsider. It's
starting to get cold up here.
On Wed, 15 Nov 2006 18:48:41 -0600, Roarmeister wrote:
I know! And there are five families that rely on this "runway" so we
really have to do something. With the sound advice I've gotten here I
feel MUCH better about the whole project coming to a happy ending. The
other parties don't know of this thread yet I'm pretty sure they will
also be put at ease when they read what we've discussed.
At present it's like a four wheel drive obstacle course. After it rains
it's very slick so sometimes you make it, sometimes you don't and you go
limping back in reverse licking your wounded pride. It just can't go on.
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